1. Field of the Invention
The present invention relates to a semiconductor memory device including a plurality of memory cell arrays each of which includes a plurality of electrically reprogrammable memory cells arranged in the form of a matrix, and an electric power supply method for such a semiconductor device.
2. Description of the Related Art
An exemplary semiconductor memory device includes a main part memory cell array and a ROM memory cell array each of which includes a plurality of electrically reprogrammable memory cells arranged in the form of a matrix, a plurality of word lines and a plurality of bit lines connected to the plurality of memory cells, a data program and read control section for, when performing data programming, read or erasure with respect to a corresponding memory cell among the plurality of memory cells, selecting a corresponding word line and a corresponding bit line among the plurality of word lines and the plurality of bit lines and applying a voltage to the selected word line and bit line, and a power supply circuit for supplying power to the data program and read control section.
The main part memory cell array has a larger capacity (about three times larger) than the ROM memory cell array.
In general, a semiconductor memory device programs, reads or erases data using several different levels of voltages. A power supply circuit for supplying power is designed and produced based on the main part memory cell array which has a larger capacity and a shorter boosting time.
A regulator circuit, which is used as a certain type of power supply circuit, oscillates easier when the capacity of the memory cell array is smaller. When the ROM memory cell array is selected to be supplied with power, an output terminal is connected to a well of a substrate in order to prevent the oscillation of the regulator circuit. The capacity of the well is used as a stabilization capacity for preventing the oscillation of the regulator circuit. In this way, in a general semiconductor memory device, the capacity of a well is used as a stabilization capacity for the regulator. Therefore, it is necessary to increase the area of the well in order to obtain a large stabilization capacity, which increases the area of the chip on which the semiconductor memory device is mounted.